Phase measurement



Bnventor Gttorneg June l, 1943. H. J. scHRADI-:R ETAL PHASE MEASUREMENT Filed sept. so,l 1941 TSU . .FU `l Tub www@ GNWWK THEODORE A. SMITH a HAROLD d Sc'HnADEn -Patented June l, i943 PHASE MEASUREMENT Harold J. Schrader, Haddon Heights, N. J., and

Theodore A. Smith, Philadelphia, Pa., assignors to Radio Corporation of America, a corporation oi' Delaware Application September 30, 1941, Serial No. 413,072

7 Claims. (Cl. 172-245) This invention relates to phase measurement. and more particularly to a method of and apparatus for determining the phase relation between two alternating voltages, the primary object of our invention being to provide an improvedmethod of and means for accurately indicating when two alternating voltages are exactly in phase.

According to our invention, the two voltages of which the phase relationship is to be indicated are first squared by any suitable means, such as a clipping circuit, then dierentiated, and then the voltage pulses so obtained are applied to two different sets of deflecting plates of a cathode ray oscillograph. The two differentiated voltages may, if desired, rst be rectied to eliminate either the positive or negative peaks before being connected to the deflecting plates, thereby simplifying the oscillograph pattern. The accuracy of the indication is controlled mainly by the steepness of the sides of the square waves produced and the degree to which the differentiated voltages are true.

The novel features that' we consider characteristic of our invention are `set forth with particularity in the appended claims. The invention itself, however, both as to itsorganization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of one embodiment thereof, when read in connection with the accompanying drawing, in which Figure 1 is a schematic diagram showing one form of our invention,

Figure 2a is a curve showing the original form of one of the two voltages being compared,

Figure 2b shows the form of the voltage after being clipped,

. Figure 2c shows the form of the voltage after being differentiated,

Figure 2d shows the diierentiated voltage of Fig. 2c after rectication, l

Figures 3a, 3b, 3c and 4d correspond to Figs. 2a, 2b, 2c and 2d, respectively, but relate to the other of the two voltages being compared,

Figures 4a, 4b, 4c and 4d show various patterns corresponding to different phase relations between the voltages of which the phase relationship is being determined.

Referring more particularly to the drawing,

there is shown, in Fig. 1, a pair of channels I square the wave into the form shown in Fig. 2b. The output from the squarlng circuit 4 is supplied to a suitable differentiating circuit l which forms the narrow voltage pulses shown in Fig. 2c. 'I'he output of the diii'erentiating circuit 6 may, if desired, be rectilled by a suitable rectifier 8 to provide the narrow rectified pulses e1 shown in Fig. 2d, and these pulses are supplied to one set of deecting plates I (for example, the vertical deilecting plates) of a cathode ray tube 9 having a screen I I. The voltage En, as shown in Fig. 3a, is supplied to an amplified I0 in the channel 3, and the output of the amplier 2 is fed to a suitable clipping circuit I2 similar to the clipping circuit 4 for` squaring the wave, as shown in Fig. 3b. The output of the clipping circuit I2 is supplied to a differentiating circuit I4 which forms the narrow voltage pulses shown in Fig. 3c at precisely the same instant as the pulses shown in Fig. 2c, and thence to a rectifier I6 which rectilies the alternating pulses of Fig. 3c to provide the narrow pulses e2 shown in Fig. 2d, the latter pulses being supplied to a second pair of deflecting plates I3 of the tube 9. The plates I3 are effective in a direction substantially normal to the direction in which the deecting plates 'I are eiiective (for example, in a horizontal direction) to deflect an electron beam I5 emitted by the cathode I8 of the tube 9. The combined effects of the deecting plates l--l and I3I3 will be to displace the electron beam I5 from its normal path to trace a pattern I1 on the screen II, and by observing the pattern I'I, the phase relation between the two voltages E1 and Ez may be quickly and accurately determined.

Any suitable amplifiers, clipping circuits, differentiating circuits and rectiers may be employed in carrying out our invention. Since these are not, per se, a part of our invention, it is not deemed necessary to describe them in greater detail. However, reference is made to the U. S. patent to Smith No. 2,132,655, granted October 11, 1938, which shows various amplifying, clipping, diiierentiating and rectifying circuits which are suitable and which may be employed in accordance with our invention.

Fig. la shows the pattern traced by the electron beam I5 when the voltage pulses e1 and e2 are exactly in phase. This pattern, it will be noted, is a straight line. When either the pulse e1 or ez leads the other by a half wave, the pattern Il will appear as a. triangle, as shown in Fig. 4b. When either of the pulses ei or e2 leads the other by only a quarter wave length, the pattern I1 will appear as a relatively wide pentagon, such as shown in Fig. 4c, while if either one of the voltage pulses e1 or e2 leads the other by only oneeighth wave length, the pattern I1 will appear as a narrower pentagon, such as shown in Fig. 4d,

the pentagon gradually approaching a straight line as the voltage pulses er and e: approach each other in phase. Thus, by observing the pattern l1. the phase relation between vthe voltages E1 and E: maybereadily determined.

From the foregoing description, it will be apparent to those skilled in the art, that we have provided a very accurate method ofv readily deter- 1. The method of determining the phase rclation between a pair of alternating voltages of thesame or harmonic'frequencies with the aid of a cathode ray tube having electron beam deflecting means eflective in two kdirections substantially normal to each other which comprises separately deriving from each of said alternating voltages other voltages having predetermined character-l istics, causing one of said last-named voltages to deflect said electron beam in one vof said directions, and simultaneously causing the other ofV said last-named voltages to defiect said electron beam in the other of said directions whereby said deriving from said deflected beam will trace a pattern on the screen of said tube indicative of the phase relation between said alternating voltages.

' 2. The method of determining the phase relation between a pair of alternating voltages of the same or harmonic frequencies with the aid of 'a cathode ray tube having electron beam defiecting means effective in two directions substantially normal to each other which comprises separately deriving predetermined voltage impulses from' each of said alternating voltages, and causing the voltage impulses so derived to deflect said electron beam from its normal path whereby 'said deflecting beam will trace a pattern on` the screen of said tube indicative of the phase relation between said alternating voltages.

3. The method of determining the phase relation between a pair of alternating voltages of the same or harmonic frequencies with the aid of a cathode ray tube having electron beam deecting means effective in two directions substantially normal to each otherl which comprises separately deriving predetermined voltage impulses from each of said alternating voltages, causing the 1 voltage impulses derived from one of said alternating voltages to deflect Vsaid electron beam in one of said directions, and simultaneously causing the 'voltage impulses derived from the other of said alternating voltages to deflect said electron beam in the other of said'directions whereby said deflected beam will trace a pattern on the screen of said tube indicative of the phase rela-l tion between said alternating voltages.

4.' The method of determining the phase relation between a pair of alternating voltages of the same or harmonic frequencies with the aid of a cathode ray tube having electron beam deflecting means effective in two directions substantially normal to each other which comprises deriving from'one of said alternating voltages a series of pulses occurring in predetermined time relation thereto, deriving from said other alternating voltage a series of .pulses occurring in a predetermined time relation with respect 4to said othery alternating voltage, causing said first-named pulses to deflect said electron beam directions, and simultaneously causing the other of said pulsesto deflect saidelectron beam in the other of said directions whereby said deflected 'beam will trace a path on the screen of said tube indicative d of the -frome one of said voltages a series of comparatively narrow voltage pulses occurring in predetermined time relation thereto, simultaneously 'other alternating voltage a series of similar pulses occurring in the same time relation with respect to said other alternating voltage, causing said first-named pulses to deflect said electron beam in one of said directions, and simultaneously causingthe other of said pulses to deflect said electron beam in the other of said directions whereby said deflected beam wil1 trace a path on the screen of saidl tube indicative of the phase relation `between said alternating voltages.

l6. The method of determining the phase relation. between a pair of alternating sinusoidal voltages of the same or the aid of a cathode ray tube having electron beam defiecting means effective in two directions substantially normal to each other which comprises separately flrst clipping each of said voltages to obtain alternating voltages of substantially square wave form, then differentiating each -of said squared voltages to obtain two sets of voltage pulses having a predetermined time relation to each of said sinusoidal voltages, then rectifying said pulses to obtain only half cycles thereof, and finally causing one set of said rectified pulses to effect displacement of said electron beam in one of said directions while simultaneously causing the other of said sets of rectified pulses to effect displacement of said electron beamA in the other of said directions whereby said deflected beam will trace a path on the screen of said tube indicative of the phase relation between said sinusoida1 voltages.

7. Inv apparatus forindicating the phase relation between a pair of alternating voltages, means providing one channel for deriving narrowvoltage impulses from one of said alternating voltages, means providing a second channel for deriving narrow voltage impulses from the other of said alternating voltages, a cathode ray tube including an electron-sensitive screen, means within said tube providing and directing an electron beam onto said screen, and means coupled to the outputs of said channels for causing said beam to be deflected in accordance with said voltage impulses to tracea pattern on said screen indicative of the phase relation between said alternating voltages.

, HAROLD J. SCI-IRADER.

THJEiODORI'l A. SMITH.

in one of said harmonic frequencies with 

